Minimally invasive surgical techniques generally attempt to perform surgical procedures while minimizing damage to healthy tissue. One particular technique for achieving this goal employs flexible surgical devices that are able to reach a target work site inside a patient by at least partially following a natural lumen, such as, for example, the digestive tract, blood-carrying lumens, or other lumens, of the patient. Following a natural lumen, for example, can allow a surgeon to operate at a work site while making fewer and/or smaller incisions through healthy tissue, although an incision may be needed at locations where the flexible device enters or leaves a natural lumen.
Surgical devices that are able to follow a natural lumen or other tortuous paths must therefore be flexible, which requires the devices to have properties and abilities that may not exist or be needed in other surgical instruments. Furthermore, although a surgical device must be flexible enough to navigate a tortuous path, in order to properly manipulate a surgical tool (e.g., an end effector) positioned at a distal end of the device, the surgical device must also provide a stable base once positioned at a work site.
In certain surgical applications and devices, however, a rigid minimally invasive instrument may be more effective for carrying out various procedures. Such instruments' inherent stiffness may be useful for tasks such as retraction, dissection, and suture tightening because a flexible device, even if prevented from bending by holding its actuating mechanisms stationary, is less stiff than a rigid instrument of similar outer diameter. As another example, if two minimally invasive instruments are used at an internal surgical work site, it is often desirable to have these instruments angled to one another so as to provide a triangulation that allows a surgeon to view the work site (e.g., using an endoscope) without the instruments blocking the view. In addition, such instrument triangulation often provides a more effective configuration for various surgical tasks (e.g., dissection, suturing, knot tying, etc.) than instruments that are oriented relatively parallel to one another.
Some conventional surgical devices that are actuatable between flexible and stiffened states have interconnected articulating links in a variety of arrangements to provide bending in one and/or multiple degrees of freedom (DOF) when in a flexible state. Such devices generally also include a force transmission mechanism (e.g., tension elements) interconnected to the links to control the bending of the device in the flexible state and to place the device in the stiffened or flexible state. Other devices may use other methods of rigidizing an instrument. For example, U.S. Patent Application Publication No. US 2009/0299343 A1 (filed May 25, 2008; entitled “Stiffening Assembly”) discloses leaf structures that may be compressed to stiffen a flexible structure. As another example, U.S. Patent Application Publication No. US 2008/0091170 A1 (filed Jun. 30, 2006; entitled “Canula System for Free Space Navigation and Method of Use”) discloses stiffening embodiments that include thermal, vacuum, and pressure stiffening methods, as well as tension element rigidizing methods. Yet another example is U.S. Patent Application No. US 2010/0160724 A1 (filed Dec. 23, 2008; entitled “Flexible Surgical Instrument with Links Undergoing Solid-State Transitions”), which discloses a long link made of a shape memory alloy or another material having one state in which the link is sufficiently flexible to bend as needed to pass through a curved entry guide and another state in which the link returns to a desired shape and is sufficiently rigid for precise controlled movement. Since these structures have a relatively large number of different parts, the costs associated with manufacturing and assembling these parts can be relatively high. Thus, flexible minimally invasive surgical instruments have certain advantages over rigid straight or curved minimally invasive surgical instruments, and vice-versa. Likewise, both instrument types have certain disadvantages in both use and construction. It is desirable, therefore, to have a single minimally invasive surgical instrument that includes the benefits of both flexible and rigid instruments while at the same time minimizing their effective disadvantages.
To navigate tight, tortuous paths and perform complex motions (e.g., at a surgical work site), it may therefore be desirable to provide a surgical device that is sufficiently flexible to follow a variously curved path in a flexible state, while also providing sufficient rigidity in a stiffened state. It may also be desirable to provide a surgical device that can transition between flexible and stiffened states, using, for example, existing actuation systems and controls. Further, it may be desirable to provide a surgical device that can transition between flexible and stiffened states, can be made of relatively simple structures, can reduce the number of components and/or differently configured components, and/or can provide for relatively robust manufacturing.